The present invention relates particularly to tire pressure monitoring devices attached to tire valve stems.
One of the most common tire-related problems is under-inflation of the tires. The tire is usually inflated when installed and not checked afterwards. Despite the notices in vehicle owner""s manuals, very few people actually check the tire pressure regularly. Driving with tire pressure that is too low will not only affect the handling characteristics of the vehicle in a negative manner but it can also be a contributing factor to tire tread separation. Lately, there have been over a hundred people killed in the United States due to vehicle rollovers which where directly related to tire tread separation. Thus, the importance of proper air pressure cannot be over-emphasized. Unless tire pressure is proper, maximum fuel efficiency cannot be obtained and a tire that is under inflated cannot meet warranty inspection as to mileage.
With the advent of a large variety of automobile tires, there is now a large variation in the recommended air pressure to be used. For example, there are many automobiles that require different inflation pressures in the front and rear tires. In addition, there are many utility vehicles that require either much higher or much lower tire pressure than customarily encountered in automobile tires. Consequently, once a car owner has inflated the tires to the proper pressure, the user must keep track of the proper pressure for each tire. After driving on the tires for awhile, the user must be able to determine when the pressure has changed in a tire sufficiently such that the user should add more air.
The present invention relates to a tire pressure monitoring device that is affixed to a tire valve stem. The tire pressure monitoring device alerts a driver when the tire pressure has dropped a predetermined amount relative to an initial tire pressure.
In certain embodiments of the invention, a tire pressure monitoring device that is installed on a tire valve stem reacts to a drop in a tire""s air pressure. For example, the device may indicate by visual, audio, electromagnetic or other means that the tire pressure has dropped by at least a predetermined amount relative to an initial tire pressure. Preferably, the device is compact and does not adversely affect the balance of a tire. In one embodiment, the tire pressure monitoring device does not utilize or rely on moving mechanical parts with the exception of the movement of a flexible membrane. Accordingly, in a preferred embodiment of the invention, centrifugal forces, dirt, debris and other road hazards do not adversely affect the operation or accuracy of the device.
In an exemplary embodiment of the present invention, the tire pressure monitoring device comprises a housing that is affixed to a tire valve stem. The housing includes two pressure chambers separated by a flexible membrane. When the device is initially attached to the tire valve, a first pressure chamber is pressurized with air pressure from the tire. This first chamber is then sealed, and the tire pressure monitoring device is now calibrated. The second chamber also is pressurized with air from the tire, but the second chamber is in constant air pressure communication with the tire. Accordingly, when the tire pressure decreases, there is a concomitant decrease in pressure within the second chamber. When the air pressure within the second chamber is less than the air pressure within the first chamber by a predetermined pressure differential, a signaling means warns the driver that the tire pressure is low.
The present invention also relates to methods of using a tire pressure monitoring device. According to one such method, the device is attached to a tire valve and subsequently calibrated. The attached device monitors the pressure differential between the air pressure within the device and the tire""s current air pressure. A warning signal is emitted when the pressure differential exceeds a predetermined pressure differential. The warning signal may be an optical signal such as a constant or flashing light, an audio signal such as from a buzzer or beeper, an electromagnetic signal such as a broadcast or transmitted analog or digital signal, an electrical signal that causes a display on the device or elsewhere to display a message relative to the change in tire pressure, or any other type of low pressure warning signal.